Aluminum-containing welding electrode

ABSTRACT

The disclosed technology generally relates to consumable electrode wires and more particularly to consumable electrode wires having a core-shell structure, where the core comprises aluminum. In one aspect, a welding wire comprises a sheath having a steel composition and a core surrounded by the sheath. The core comprises aluminum (Al) at a concentration between about 3 weight % and about 20 weight % on the basis of the total weight of the welding wire, where Al is in an elemental form or is alloyed with a different metal element. The disclosed technology also relates to welding methods and systems adapted for using the aluminum-comprising electrode wires.

BACKGROUND Field

The disclosed technology generally relates to consumable weldingelectrodes wires and more particularly to aluminum-containing consumablewelding electrode wires, and to welding methods and systems adapted forusing the aluminum-containing electrode wires.

Description of the Related Art

Various welding technologies utilize welding wires that serves as asource of metal. For example, in metal arc welding, an electric arc iscreated when a voltage is applied between a consumable weld electrodewire, which serves as one electrode that advances towards a workpiece,and the workpiece, which serves as another electrode. The arc melts atip of the metal wire, thereby producing droplets of the molten metalwire that deposit onto the workpiece to form a weldment or weld bead.

Technological and economic demands on welding technologies continue togrow in complexity. For example, the need for higher bead quality inboth appearance and in mechanical properties continues to grow,including high yield strength, ductility and fracture toughness.Simultaneously, the higher bead quality is often demanded whilemaintaining economic feasibility. Some welding technologies aim toaddress these competing demands by improving the consumables, e.g. byimproving the physical designs and/or compositions of the electrodewires.

One approach to addressing such competing demands is to incorporateadditives into consumable electrodes. An example additive is chromium(Cr), which may be added to improve oxidation/corrosion resistance ofthe resulting weldment. However, the addition of such additives may beinsufficient to simultaneously satisfy a set of competing weldmentcharacteristics, which may include, e.g., resistance to hot cracking andhigh fracture toughness, in addition to corrosion resistance. Inaddition, the set of competing weldment properties may need to besatisfied while maintaining economic feasibility, which may be difficultwhen main additives include relatively expensive elements such Cr. Inthe following, various embodiments of consumable welding electrodewires, welding processes and systems capable of satisfying these andother competing weldment characteristics, as well as productivity andeconomic considerations, are described.

SUMMARY

The disclosed technology generally relates to consumable weldingelectrodes wires and more particularly to aluminum-containing weldingconsumable electrode wires having a core-shell structure, where the corecomprises aluminum. The disclosed technology also relates to weldingmethods and systems adapted for using the aluminum-comprising electrodewires.

In one aspect, a welding wire is configured to serve as a source of weldmetal during welding, e.g., flux-cored arc welding (FCAW). The weldingwire comprises a sheath having a steel composition and a core surroundedby the sheath. The core comprises aluminum (Al) at a concentrationbetween about 3 weight % and about 20 weight % on the basis of the totalweight of the welding wire, where Al is in an elemental form or isalloyed with a different metal element.

In some embodiments, the sheath and the core are configured such that aweld bead formed using the welding wire has aluminum (Al) at aconcentration between about 4 weight % and about 6.5 weight % andmanganese (Mn) at a concentration between about 15 weight % and about 25weight %. In some other embodiments, the sheath and the core areconfigured such that a weld bead formed using the welding wire has afracture toughness greater than 20 ft-lbs. when measured at atemperature lower than 0° F. In some other embodiments, the sheath andthe core are configured such that a weld bead formed using the weldingwire has a ferrite number between 1 and 125.

In another aspect, a welding wire configured to serve as a source ofweld metal during welding, e.g., flux-cored arc welding (FCAW),comprises a core surrounded by a sheath and a composition such that aweld bead formed using the welding wire has iron (Fe) at concentrationbetween about 50 weight % and about 85 weight % and aluminum (Al) at aconcentration between about 3 weight % and about 20 weight %.

In another aspect, a method of welding, e.g., flux-cored arc welding(FCAW), comprises providing a welding wire configured to serve as asource of weld metal during welding. The welding wire comprises a sheathhaving a steel composition and a core surrounded by the sheath. The corecomprises aluminum (Al) at a concentration between about 3 weight % andabout 20 weight % on the basis of the total weight of the welding wire,wherein Al in an elemental form or is alloyed with a different metalelement. The method additionally comprises applying sufficient energy toproduce a steady stream of droplets of molten welding wire. The methodfurther comprises depositing the molten droplets onto a workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a configuration of electrodes in ametal arc welding process.

FIG. 2A illustrates a metal arc welding system configured for aself-shielded flux-cored arc welding (FCAW-S), according to embodiments.

FIG. 2B illustrates a metal arc welding system configured for agas-shielded flux-cored arc welding (FCAW-G), according to embodiments.

FIG. 3A is a schematic illustration of a flux-cored electrode wirecomprising aluminum in the core, according to embodiments.

FIG. 3B is a schematic illustration of a flux-cored electrode wirecomprising aluminum in the core, according to embodiments.

FIG. 3C is a schematic illustration of a flux-cored electrode wirecomprising aluminum in the core, according to embodiments.

FIG. 3D is a schematic illustration of a flux-cored electrode wirecomprising aluminum in the core, according to embodiments.

FIG. 4A is a nickel equivalent versus aluminum content for weldmentshaving various ferrite numbers produced from flux-cored electrode wires,according to embodiments.

FIG. 4B is a scanning electron micrograph of a weldment having ferritenumber 2 in FIG. 4A, according to embodiments.

FIG. 4C is a scanning electron micrograph of a weldment having ferritenumber 13 in FIG. 4A, according to embodiments.

FIG. 4D is a scanning electron micrograph of a weldment having ferritenumber 33 in FIG. 4A, according to embodiments.

FIG. 4E is a scanning electron micrograph of a weldment having ferritenumber 123 in FIG. 4A, according to embodiments.

FIG. 5 is a schematic illustration of a metal arc welding systemconfigured for flux-core arc welding using a flux-cored electrode wirecomprising aluminum in the core, according to embodiments, according toembodiments.

FIG. 6 is a flow chart of a method of flux-core arc welding using aflux-cored electrode wire comprising aluminum in the core, according toembodiments.

DETAILED DESCRIPTION

Various technological and economic demands on welding technologies,which are often competing demands, continue to grow in complexity. Forexample, higher bead quality in terms of both appearance and mechanicalproperties are often desired without incurring negative economic orproductivity consequences, e.g. higher cost of raw material and/orwelding. In particular, in steel-based welding, improving or satisfyingcompeting characteristics of mechanical properties such as yieldstrength, ductility, corrosion resistance, resistance to hot crackingand fracture toughness, may be needed, while maintaining economicfeasibility.

Some welding technologies aim to address these competing demands byimproving the consumables, e.g. by improving the physical designs and/orcompositions of consumable electrode wires. As one example, sometraditional consumable electrodes incorporate additives such as chromium(Cr) and nickel (Ni). Chromium and nickel addition to ferrous alloys canprovide, e.g., oxidation resistance through the ability to form aprotective oxide layer. However, high amounts of Cr and Ni may beundesirable from a cost point of view. In addition, while providing oneadvantage, some additives may be insufficient in satisfying othercharacteristics, e.g., competing characteristics, or may introduceundesirable consequences. For example, under some circumstances, whileproviding oxidation and corrosion resistance, relatively high amounts ofCr and Ni can promote an undesirable amount of body-centered cubic (BCC)ferrite in the resulting weldment, which may lead to undesirablemechanical properties, including lower fracture toughness.

In various embodiments described herein, consumable electrode wires havea core-shell structure, where aluminum is present in particular amounts,e.g., in the core. The electrodes various satisfy competing weldmentproperties, such as corrosion resistance, resistance to hot cracking andhigh fracture toughness. In addition, when used in certain weldingprocesses, e.g., flux-cored arc welding, the disclosed electrodes canprovide a lower cost solution compared to traditional additives insteel-based welding wires.

Welding Processes for Using Aluminum-Containing Welding Electrodes

FIG. 1 is a schematic illustration of a configuration of electrodes inmetal arc welding processes. In metal arc welding, e.g., gas-metal arcwelding (GMAW), an electric arc is created between a consumable metalwire 6, which is electrically connected to one electrode 4 (e.g., anode(+)), and a workpiece 2, which serves as another electrode (e.g.,cathode (−)). Thereafter, a plasma 8 is sustained, which containsneutral and ionized gas molecules, as well as neutral and chargedclusters or droplets of the material of the metal wire 6 that have beenvaporized by the arc. During welding, the consumable metal wire 6 isadvanced toward the work piece 2, and the resulting molten droplets ofthe metal wire 6 deposits onto the workpiece, thereby forming a weldbead.

The metal wire 6 may be a welding wire comprising aluminum (Al) at aconcentration between about 4 weight % and about 8 weight % on the basisof the total weight of the metal wire 6, according to variousembodiments. In some embodiments, the metal wire 6 comprises a sheathhaving a steel composition and a core surrounded by the sheath, wherethe core comprises aluminum (Al) at a concentration between about 4weight % and about 8 weight % on the basis of the total weight of thewelding wire. The metal wire 6 can be used in various arc weldingprocesses, including gas-metal arc welding processes, which may employeither solid electrode wires (GMAW) or metal-cored wires (GMAW-C). Themetal wire 6 can also be used in flux-cored arc welding processes(FCAW), which can be gas shielded flux-cored arc welding (FCAW-G) orself-shielded flux-cored arc welding (FCAW-S). The metal wire 6 canfurther be used in shielded metal arc welding (SMAW) processes andsubmerged arc welding (SAW) processes, among others. In the followingdifferent welding processes that may employ the metal wire 6 aredescribed in more detail.

In gas-metal arc welding using solid (GMAW) or metal-cored electrodes(GMAW-C), a shielding gas is used to provide protection for the weldpool and the weld bead against atmospheric contamination during welding.When solid electrodes are used, they are appropriately alloyed withactive ingredients that, in combination with the shielding gas, may bedesigned to provide low porosity or porosity-free welds with the desiredphysical and mechanical properties of the resulting weld bead. Whenmetal-cored electrodes are used, some of the active ingredients may beadded in the core of a metallic outer sheath, and designed to provide asimilar function as in the case of solid electrodes.

Solid and metal-cored electrodes are designed to provide, underappropriate gas shielding, a solid, substantially porosity-free weldmentor beads with yield strength, tensile strength, ductility and impacttoughness to perform satisfactorily in the final applications. Theseelectrodes may also be designed to minimize the quantity of slaggenerated during welding. For some applications, metal-cored electrodescan be used as an alternative to solid wires to increase productivity.As described herein, metal-cored electrodes refer to compositeelectrodes having a core that is at least partially filled andsurrounded by a metallic outer sheath. The core can include metal powderand active ingredients to help with arc stability, weld wetting andappearance and desired physical and mechanical properties. Themetal-cored electrodes are manufactured by mixing the ingredients of thecore material and depositing them inside a formed strip, and thenclosing and drawing the strip to the final diameter. For someapplications, cored electrodes can provide increased deposition ratesand a wider, relatively consistent weld penetration profile compared tosolid electrodes. As described herein, metal-cored electrodes (GMAW-C)refer to electrodes having a core whose ingredients are primarilymetallic. When present, nonmetallic components in the core have acombined concentration less than 5%, 3% or 1%, on the basis of the totalweight of each electrode. The relatively low nonmetallic components maydistinguish GMAW-C electrodes from flux-cored arc welding electrodesdescribed in more detail, infra. The GMAW-C electrodes can becharacterized by a spray arc and high quality weld metal.

Similar to gas-metal arc welding using metal-cored electrodes (GMAW-C),electrodes used in flux-cored arc welding (FCAW, FCAW-S, FCAW-G) alsoinclude a core surrounded by a shell. That is, the cored electrodes usedin flux-cored arc welding have a core that is at least partially filledand surrounded by a metallic outer sheath, similar to metal-coredelectrodes described above. However, unlike metal-cored electrodes(GMAW-C), the cored electrodes used in flux-cored arc welding (FCAW)additionally includes fluxing agents designed to provide protection forthe weld pool and the weld bead against atmospheric contamination duringwelding, at least partially in lieu of a shielding gas. The coredelectrodes used in flux-cored arc can additionally include other activeingredients to help with arc stability, weld wetting and appearance anddesired physical and mechanical properties. In one aspect, flux-coredarc electrodes may be distinguished from metal-cored electrodes by theamount of nonmetallic components present in the core, whose combinedconcentration can be less than 5%, 3% or 1%, on the basis of the totalweight of each electrode.

A large number of fluxing agent compositions for flux-cored electrodeshave been developed to control the arc stability, modify the weld metalcomposition, and to provide protection from atmospheric contamination.In flux-cored electrodes, arc stability may be controlled by modifyingthe composition of the flux. As a result, it may be desirable to havesubstances which serve well as plasma charge carriers in the fluxmixture. In some applications, fluxes can also modify the weld metalcomposition by rendering impurities in the metal more easily fusible andproviding substances with which these impurities may combine. Othermaterials are sometimes added to lower the slag melting point, toimprove slag fluidity, and to serve as binders for the flux particles.Various wires used in FCAW may share some similar characteristics, e.g.,forming a protective slag over the weld, using a drag angle technique,having the ability to weld out-of-position or flat and horizontal athigher deposition rates, having the ability to handle relatively higheramount of contaminants on the plate, etc. On the other hand, differenttypes of flux-cored arc welding processes exist, namely: self-shieldedflux-cored arc welding (FCAW-S) and gas-shielded flux-cored arc welding(FCAW-G), which are described in more detail below in reference to FIGS.2A and 2B

FIGS. 2A and 2B illustrate systems 20A and 20B configured for a FLAW-Sprocess and a FCAW-G process configured to use the aluminum-containingelectrode wires, respectively, according to embodiments. In a FCAWprocess, a plasma 8 is produced by an electric arc that is createdbetween a FCAW-S wire 26A (FIG. 2A) or a FCAW-G wire 26B (FIG. 2B),which is electrically connected to one electrode 4 (e.g., one of ananode (+) or a cathode (−)), and a workpiece 2, which serves as anotherelectrode (e.g., the other of the anode (+) and the cathode (−)).Thereafter, a plasma 8 is sustained, which contains neutral and ionizedgas molecules, as well as neutral and charged clusters or droplets ofthe material of the metal wire 6 that have been vaporized by the arc. Inoperation, the FCAW-S wire 26A (FIG. 2A) and the FCAW-G wire 26B (FIG.2B) advance towards the work piece 2, and the molten droplets from thewires deposit onto the workpiece 2, thereby forming a weld bead orweldment 24 comprising a solidified weld metal. Unlike the FCAW-S system20A (FIG. 2A), the FCAW-G system 20B also include a shielding gas inlet28 for supplying a shielding gas 27 for delivery to the plasma regionthorough a shielding gas nozzle 27.

Referring to FIG. 2A, FCAW-S processes utilize a protective slag andgases produced from chemical reactions in the arc itself to protect themolten metal from the atmosphere. The flux ingredients in the core ofthe FCAW-S wire 26A perform multiple functions, including deoxidizingand denitrifying the molten metal, forming a protective slag, which alsoshapes the bead and can hold molten metal out-of-position, and addingalloying elements to the weld bead 24 to produce desired properties andcontrollably affecting various welding characteristics (e.g., deeppenetration characteristics and high deposition rates), among otherfunctions.

Under some circumstances, FCAW-S processes/systems according toembodiments provide increased productivity compared to other processes,e.g., a stick (i.e., manual) welding, resulting in part from relativelyhigher deposition rate capabilities with a semi-automatic process forsimilar or same applications as applications where stick electrodes areused. For example, some FCAW-S are adapted for outdoor welding that doesnot use external shielding gas, especially where the shielding gas caneasily be blown away by wind and result in porosity in the resultingweld bead with gas-shielded processes. However, embodiments are not solimited and other FCAW-S processes can be adapted for indoor welding.

Some FCAW-S processes according to embodiments are performed under a DC−polarity. Some FCAW-S processes according to embodiments have a globulararc transfer, ranging from fine droplets to large droplets of metal.

Referring to FIG. 2B, FCAW-G processes use both a slag system and anexternal shielding gas to protect the arc from the atmosphere. Exampleshielding gases that may be used include carbon dioxide (CO₂), e.g.,essentially pure CO₂ or a mixture of CO₂ and inert gas, e.g., 75-85%argon (Ar) combined with a balance of CO₂. Similar to FCAW-S wires, thecore ingredients of FCAW-G wires may be configured to produce a slag, toincorporate alloying elements to the weld bead and to affect the weldingcharacteristics. However, unlike the FCAW-S wires, the FCAW-G wires mayderive protection of the molten metal from the atmosphere primarily oressentially through the external shielding gas 27 delivered around theplasma region.

Still referring to FIG. 2B, some FCAW-G processes are characterized bysmall droplet arc transfer with a smooth, spray arc. Some FCAW-Gprocesses according to embodiments are performed under DC+ polarity.Some FCAW-G systems/processes are more adapted, e.g., compared to FCAW-Sprocesses, for indoor welding, as they have smoother arccharacteristics. However, embodiments are not so limited and some FCAW-Gprocesses can be adapted for outdoor welding.

Aluminum-Containing Welding Electrodes

Various embodiments disclosed herein aim to address the increasinglycomplex and competing characteristics of weld beads resulting fromvarious welding processes described above. The competing characteristicsinclude high toughness, e.g., high toughness at low temperatures, smallstatistical scatter of toughness, low tendency for hot cracking and lowporosity, among other characteristics. Furthermore, thesecharacteristics may be constrained by economic considerations, e.g., thecost of consumable electrodes. To address these and other needs,aluminum-containing electrodes are cored electrodes, according tovarious embodiments.

As described above, cored electrodes are composite electrodes having asheath formed of, e.g., a steel composition, with a core of particleshaving specifically selected iron and other metal powders and alloys.Additives such as stabilizers and arc enhancers can be added easilyduring manufacturing, providing a wider operating window for the welder.

A cored electrode is a continuously fed tubular metal sheath with a corethat can include particles or powders. The core may include fluxingelements, deoxidizing and denitriding agents, and alloying materials, aswell as elements that increase toughness and strength, improve corrosionresistance, and stabilize the arc. As described above, a cored electrodecan be categorized as one of the following: metal-cored electrodes(GMAW-C), self-shielded flux-cored electrodes (FCAW-S) and gas-shieldedflux-cored electrodes (FCAW-G).

Because of the flexibility in manufacturing, when a job calls forspecial electrodes, cored electrodes can be more economical than solidelectrodes. Because the manufacturing process involves blending metalpowders instead of creating a special melt of steel, small quantitiesare easier to produce, and minimum order quantities are much lower. As aresult, cored electrodes can be produced with shorter turnaround timesand at lower cost than special-ordered solid electrodes. Thus, in thefollowing, various embodiments of electrode wires including analuminum-containing core surrounded by a sheath are described.

In one aspect of various embodiments disclosed herein, a balance betweenthese competing characteristics can be achieved in part by configuringthe welding wire such that the resulting weld bead contains a controlledamount of austenite. As described herein, a weld bead having acontrolled-fraction of FCC austenite refers to a weld bead formed from aweld wire to have greater than 20%, 30% or 40%, or to have percentage ina range defined by these percentages, by weight of the weld bead. Theinventors have found that, advantageously, having the controlled amount(e.g., >30% by weight) of austenite, when achieved at least in part witha relatively high concentration of aluminum and various other elementsin the weld bead as described infra, a balance between the variouscompeting technical needs as well as the cost constraints can besatisfied. Thus, advantageously, embodiments disclosed herein relate toelectrodes, e.g., cored electrodes, comprising aluminum (Al) at aconcentration between about 4 weight % and about 8 weight % on the basisof the total weight of the welding wire. The weld beads resulting fromthe aluminum-containing electrodes achieves, among othercharacteristics, low porosity, high fracture toughness at lowtemperatures and high resistance to hot cracking. As described herein,high fracture toughness refers to a fracture toughness value greaterthan about 20, 50, 100, 150 or 200 ft-lbs., as measured using Charpyimpact test known in the relevant industry. As described herein, lowtemperature fracture toughness refers to fracture toughness measured attemperatures below about 0° F., −20° F., or −40° F.

FIGS. 3A-3D schematically illustrate welding electrode wires 30A-30Dcomprising aluminum-containing cores 38 a-38 d surrounded by a sheath 34and configured to serve as an electrode during metal arc welding,according to embodiments. The welding electrode wires 30A-30D includes asheath 34 having a first base metal composition and cores 38 a-38 dsurrounded by the sheath 34, where the cores 38 a-38 d comprise a secondbase metal composition and various other elements described infra, whosecombination is adapted for forming a weld bead having controlled amountsof the austenite phase. In particular, the cores 38 a-38 d includealuminum (Al) at a concentration between about 4 weight % and about 8weight % on the basis of the total weight of the welding wire, where Alis in an elemental form or is alloyed with a different metal element. Invarious embodiments, compositions of the first base metal of the sheath34 and the second base metal of the cores 38 a-38 d are the same, whilein other embodiments, the compositions of first base metal and thesecond base metal are different.

In various embodiments of the electrode wires 30A-30D, the one or bothof the first and second base metal compositions comprise a steelcomposition. In some embodiments, the base metal composition can be acarbon steel composition. Non-limiting example carbon steel compositionsinclude Fe and one or more of C at a concentration between about 0.01 wt% and about 0.5 wt %, Si at a concentration between about 0.1 wt % andabout 1.5 wt %, Mn at a concentration between about 0.5 wt % and about 5wt %, S at a concentration between about 0.001 wt % and about 0.05 wt %,P at a concentration between about 0.001 wt % and about 0.05 wt %, Ti ata concentration between about 0.01 wt % and about 0.5 wt %, Zr at aconcentration between about 0.01 wt % and about 0.5 wt %, Al at aconcentration between about 0.01 wt % and about 0.5 wt % and Cu at aconcentration between about 0.1 wt % and about 1 wt %.

In some other embodiments, one or both of the first and second basemetal compositions can be a low-carbon steel composition. Somenon-limiting examples include compositions having C at a concentrationless than about 0.10 wt % and Mn at a concentration up to about 0.4 wt%, and compositions having C at a concentration less than about 0.30 wt% and Mn at a concentration up to about 1.5 wt %.

In some other embodiments, one or both of the first and second basemetal compositions can be a low-alloy steel composition. To provide somenon-limiting example compositions, a low-alloy steel compositionincludes Fe and one or more of C at a concentration between about 0.01wt % and about 0.5 wt %, Si at a concentration between about 0.1 wt %and about 1.0 wt %, Mn at a concentration between about 0.5 wt % andabout 5 wt %, S at a concentration between about 0.001 wt % and about0.05 wt %, P at a concentration between about 0.001 wt % and about 0.05wt %, Ni at a concentration between about 0.01 wt % and about 5 wt %, Crat a concentration between about 0.1 wt % and about 0.5 wt %, Mo at aconcentration between about 0.1 wt % and about 1 wt %, V at aconcentration between about 0.001 wt % and about 0.1 wt %, Ti at aconcentration between about 0.01 wt % and about 0.5 wt %, Zr at aconcentration between about 0.01 wt % and about 0.5 wt %, Al at aconcentration between about 0.01 wt % and about 0.5 wt % and Cu at aconcentration between about 0.1 wt % and about 1 wt %.

In some other embodiments, one or both of the first and second basemetal compositions can be a stainless steel composition. To provide somenon-limiting example compositions, a stainless steel compositiontypically includes Fe and one or more of C at a concentration betweenabout 0.01 wt % and about 1 wt %, Si at a concentration between about0.1 wt % and about 5.0 wt %, Cr at a concentration between about 10 wt %and about 30 wt %, Ni at a concentration between about 0.1 wt % andabout 40 wt %, Mn at a concentration between about 0.1 wt % and about 10wt %, S at a concentration between about 0.001 wt % and about 0.05 wt %and P at a concentration between about 0.001 wt % and about 0.05 wt %.

Without being bound to any theory, various elements incorporated in thefirst and/or second above can provide particular advantages in steelwelding, as discussed herein to provide few examples. For example, asdiscussed further below, carbon, manganese, nickel and copper can eachserve to stabilize the austenite phase, which in turn can improvefracture toughness in the weldment, which can be an indicator ofstrength and ductility. Manganese can further serve as a deoxidizerwhich removes oxygen from the weld and reduces weld metal porosity.Copper can be added intentionally as part of the manufacturing processcan be present as a result of coating of the wire electrodes (ifcopper-coated) for improved conductivity, and therefore, better arcinitiation between the welding electrode and the contact tip.

Without being bound to any theory, as discussed further below, aluminum,silicon, chromium and molybdenum can serve as a ferrite-stabilizingelement, which can in turn improve hot cracking performance of theweldment. Silicon can also serve as a deoxidizer which removes oxygenfrom the weldment, and reduce weld metal porosity. In general, thehigher the level of silicon in the metal, the more fluid the weldpuddle. Additions of silicon can also increase tensile and yieldstrength. Chromium can also improve corrosion resistance. Molybdenum canalso add strength and improve impact properties, even when the weld issubject to stress relieving post-weld heat treatment.

Without being bound to any theory, phosphorus is generally undesirableto the weld deposit, as it can contribute to weld cracking. Sulfur isalso generally undesirable for weldability and can contribute to weldcracking. However, in limited amounts, sulfur or phosphorus can improvefluidity and wetting of the weld puddle.

Without being bound to any theory, titanium can serve as aferrite-stabilizing element and as a deoxidizer and/or a denridizer.Zirconium can serve as a deoxidizer.

To achieve various advantageous characteristics of the weld processand/or the weld bead describe herein, welding wires 30A-30D include thecores 38 a-38 d having relatively high amounts of aluminum (Al) andmanganese (Mn), according to embodiments. In various embodiments, thecores 38 a-38 d comprise Al at a concentration between about 1 weight %and about 20 weight %, between about 2 weight % and about 15 weight %,between about 3 weight % and about 10 weight %, between about 4 weight %and about 8 weight %, or a concentration within a range defined by anyof these values, for instance about 5 weight %, on the basis of thetotal weight of the welding wire, according to embodiments. The core 38additionally comprises manganese (Mn) at a concentration between about 1weight % and about 60 weight %, between about 5 weight % and about 40weight %, between about 10 weight % and about 30 weight %, or aconcentration within a range defined by any of these values, forinstance about 18 weight %, on the basis of the total weight of thewelding wire. In some embodiments, welding wires 30A-30D include thecores 38 a-38 d having a combination of concentrations where Alconcentration is between about 3 weight % and 20% and Mn concentrationis between about 10% and 60%, Al concentration is between about 8 weight% and 20% and Mn concentration is between about 30% and 60%, where Alconcentration is between about 9 weight % and 20% and Mn concentrationis between about 35% and 60%, or where Al concentration is between about10 weight % and about 20% and Mn concentration is between 40% and about60%.

In various embodiments, each of Al and Mn is in an elemental form or isalloyed form with a different metal element. For example, when in analloyed form, Al and/or Mn may be present as part of a metallic alloycompound, e.g., MMg, MSi MZr, MFe, where M is Al or Mn, such as AlMg,AlSi, AlZr, FeMn, FeMnSi, or MnSi, among other metallic alloy compounds.Without being bound to any theory, the presence of Al in the core 38 ain amounts disclosed herein, alone or in combination with otherelements, can provide various advantages in the resulting weld bead. Forexample, similar to Cr, when present within the disclosed range, Al canadvantageously provide superior oxidation resistance of the resultingweldment.

In addition, Al in particular amounts described herein, alone incombination with other elements, can advantageously provide relativelylow porosity in the resulting weldment, thereby providing wider processwindows, e.g., providing a wider range of deposition rate.

In addition, Al in particular amounts described herein, alone or incombination with other elements, can serve as deoxidizing and/ordenitridizing agents such that the resulting weld bead has nitrogen (N)or oxygen (O) at a concentration greater than zero weight % and lessthan about 1 weight %, greater than zero weight % and less than about0.5 weight %, or greater than zero weight % and less than about 0.1weight %, for instance about 0.2 weight %, on the basis of the totalweight of the weld bead, according to embodiments.

As described herein, austenite refers to a face center cubic (FCC) phaseof iron atomic structure which can contain up to about 2% carbon insolution. As described herein, ferrite refers to a body center cubic(BCC) phase of iron which can hold very little carbon; typically 0.0001%at room temperature. It can exist as either an alpha or delta ferrite.The inventors have recognized that the advantages of having controlledand balanced amounts of the FCC phase and the BCC phase, which may beassociated with the various desirable bead characteristics describedherein, can be realized by having relatively high amounts of Al alone orin combination with various other elements as describe herein. Havingcontrolled amounts of the FCC and BCC phases in the weld beads can bedesirable because, e.g., without being bound to any theory, relativelyhigh ferrite content can be associated with relatively poor lowtemperature fracture toughness, while being associated with relativelysuperior hot or solidification cracking performance. In contrast,relatively low ferrite content can be associated with relativelysuperior low temperature fracture toughness while being associated withrelatively poor hot or solidification cracking performance. As describedherein, standardized expression known as the ferrite number (FN), whosevalues range from 1 to 125, adopted by the Welding Research Council(WRC), the American Welding Society (AWS), and other agencies, is usedto describe the relative amount of ferrite in the weldment.

The inventors have recognized that Al, when present in relatively highconcentrations, can be a stabilizer for the BCC phase of iron, orferrite. That is, the concentration of Al can be proportional to thestability or the amount of the BCC phase of iron. Thus, in variousembodiments disclosed herein, the BCC-stabilizing effect of Al can be atleast partially offset using one of more FCC phase or austenitestabilizing elements in iron, e.g., Ni, Mn, Cu, Co, C and/or N, asdescribed below.

In particular, without being bound to any theory, Mn in particularamounts described herein, alone or in combination with other elementsincluding Al having the amounts described above, can balance the amountsof FCC and BCC phases to produce a weld bead having a relatively highfracture toughness, e.g., greater than about 20, 50, 100, 150 or 200ft-lbs., as measured using Charpy impact test, when measured attemperatures below about 0° F., −20° F. or −40° F., at least in part dueto the presence of relatively high amounts of austenite. In addition, Mnin particular amounts described herein can produce a weld bead withrelatively low scatter in measured fracture toughness values. Forexample, under some circumstances, the measured fracture toughnessvalues display a bimodal distribution having a high toughnessdistribution and a low toughness distribution. According to embodiments,greater than 80% or 90% of the measured data points are included in thehigh toughness distribution, while the remaining data points areincluded in the low toughness distribution.

Under some circumstances, the inventors have found that it can becritical to have a concentration of Al that does not exceed about 20weight %, about 15 weight %, or about 10 weight %, on the basis of thetotal weight of the welding wire. In addition, it can be critical thatthe concentration of Mn exceed about 1 weight %, about 5 weight % orabout 10 weight %, on the basis of the total weight of the welding wire.In addition, under some circumstances, the inventors have found that itcan be critical to have a concentration of Al that exceeds about 1weight %, about 2 weight %, or about 3 weight %, on the basis of thetotal weight of the welding wire. In addition, it can be critical thatthe concentration of Mn does not exceed about 30 weight %, about 40weight % or about 50 weight %, on the basis of the total weight of thewelding wire. When the combination of concentrations of Al and Mn arecontrolled as described, a combination of desirable characteristicsincluding high fracture toughness, low porosity and resistance to hotcracking can be achieved.

In addition, in some embodiments, the cores 38 a-38 d of the cored wires30A-30D further comprise nickel (Ni) at a concentration greater thanzero weight % and less than about 50 weight %, greater than zero weight% and less than about 20 weight %, greater than zero weight % and lessthan about 10 weight %, or greater than zero weight % and less thanabout 10 weight %, for instance about 2 weight %, on the basis of thetotal weight of the welding wire. In some embodiments, the core 38 a-38d of the cored wires 30A-30D further comprises one or more of copper(Cu) and cobalt (Co) at a concentration greater than zero weight % andless than about 10 weight %, greater than zero weight % and less thanabout 5 weight %, or greater than zero weight % and less than about 2weight, for instance about 5 weight %, on the basis of the total weightof the welding wire.

In some embodiments, the cores 38 a-38 d of the cored wires 30A-30Dfurther comprise carbon (C) at a concentration greater than zero weight% and less than about 5 weight %, greater than zero weight % and lessthan about 2.5 weight %, or greater than zero weight % and less thanabout 1 weight %, for instance about 0.2%, on the basis of the totalweight of the welding wire. In some embodiments, the core 38 of thecored wire 30A further comprises nitrogen (N) at a concentration greaterthan zero weight % and less than about 4 weight %, greater than zeroweight % and less than about 2 weight %, or greater than zero weight %and less than about 1 weight %, for instance about 0.2 weight %, on thebasis of the total weight of the welding wire.

In some embodiments, the cores 38 a-38 d having particular combinationsof the various elements give rise to the various desirable attributesdescribed above. In particular, the inventors have found that the cores38 a-38 d of the welding wires 30A-30D comprise a combination of Mn, Ni,C, Ni, Cu and Co, which can collectively serve to stabilize the FCCphase in the weldment, among other effects. In particular, the inventorshave found that a measure of the amount of FCC-stabilizing elements canbe expressed by an equivalent nickel concentration, Ni_(eq), describedby the following formula:Ni_(eq)=2[Mn]+[Ni]+30[C]+20[N]+0.3[Cu]+0.3[Co]  [1]In various embodiments, the Ni_(eq) is between about 10 weight % andabout 80 weight %, between about 20 weight % and about 70 weight % orbetween about 30 weight % and about 60 weight %, where [Mn], [Ni], [C],[N], [Cu] and [Co] represent weight % of respective elements. In Eq.[1], ratios of the elements can vary within +/−20%, 10% or 5%, accordingto embodiments. For example, the ratio of manganese to nickel can be2.0+/−0.4, 2.0+/−0.2 or 2.0+/−0.1.

As described above, various austenite-stabilizing elements including Mn,Ni, C, N, Cu and Co can be included in the core to control the relativefraction of austenite in the resulting weld bead, among othercharacteristics. In some embodiments, the cores 38 a-38 d of theelectrode wires 30A-30D, respectively, may further include, withoutbeing bound to any theory, elements that may be active in stabilizingthe ferrite phase. Accordingly, in some embodiments, the cores 38 a-38 dof the electrode wires 30A-30D additionally includes one or more offerrite-stabilizing elements selected from the group consisting ofchromium (Cr), molybdenum (Mo), silicon (Si), titanium (Ti), niobium(Nb), vanadium (V) and tungsten (W) such that the weld bead has a totalconcentration of the ferrite-stabilizing elements that is greater than 0weight % and less than about 20 weight %, greater than 0 weight % andless than about 10 weight %, or greater than 0 weight % and less thanabout 5 weight % according to embodiments.

Thus, in various embodiments of core-electrode wires 30A-30D describedherein, the cores 30 a-30 d includes aluminum. In addition, the cores 30a-30 d may include one or more austenite-stabilizing elements selectedfrom the group consisting of Mn, Ni, C, N, Cu and Co and/or one or moreferrite-stabilizing elements selected from the group consisting of Cr,Mo, Si, Ti, Nb, V and W.

According to embodiments, the above-described concentrations on thebasis of the total weight of the welding wire can be achieved at leastin part by configuring the metal-cored electrodes 30 a/30 b to have anouter diameter (OD) between 0.045″ (1.1 mm) and 0.068″ (1.7 mm), between0.045″ (1.1 mm) and 3/32″ (2.4 mm) or between 0.052″ (1.4 mm) and 0.068″(1.7 mm).

According to embodiments, the above-described concentrations can beachieved at least in part by configuring the contents of the core 38a/38 b/38 c/38 d and the sheath 34, such that the contents of the coreconstitute, on the basis of the total weight of the metal coredelectrode wires 30 a/30 b/30 c/38 d, between about 1 wt % and about 80wt %, between about 10 wt % and about 50 wt %, or between about 15 wt %and about 30 wt %.

According to embodiments, various embodiments disclosed herein can beoptimized for any one of metal-cored (GMAW-C) electrodes, self-shieldedflux-cored (FCAW-S) electrodes and gas-shielded flux-cored (FCAW-G)electrodes.

In the above, embodiments of the cored electrodes 30A-30D have beendescribed without particular reference to the structure of the cores 38a-38 d. The cored electrode 30A can, e.g., have the core 38 a configuredas a solid or as a volume filled with powder. In the following, inreference to FIGS. 3B-3D, embodiments of welding electrode wires 30B,30C, 30D having respective cores 38 b, 38 c, 38 d arranged to includedifferently arranged powders are described. In particular, each of thecores 38 b, 38 c, 38 d is at least partially filled with particlescomprising various elements described above and a second base metalcomposition as described above, whose combination is adapted for forminga weld bead having a controlled fraction of the austenite phase. Theparticles in cored electrodes that include Al and austenite-stabilizingelements and/or ferrite-stabilizing elements generally include metal andalloy particles, rather than compound particles other than metal andalloy particles, such as oxides or fluoride particles, and areconfigured to produce relatively small islands of slag on the face ofthe resulting weld beads. However, embodiments are not so limited, andAl and austenite-stabilizing element and/or ferrite-stabilizing elementscan be in the form of compounds such as oxides, nitrides and fluorides.

In the illustrated embodiment of FIG. 3B, particles 32 are substantiallyuniform in composition. That is, each of the particles 32 contains thesecond base metal including any one of the steel compositions describedabove, and aluminum. Each of the particles can also include one or moreaustenite-stabilizing elements and/or one or more ferrite-stabilizingelements, as described above. The illustrated configuration may result,e.g., when the particles 32 are produced from the same alloy ingot.

Still referring to FIG. 3B, particles 32 are formed of an alloy of thesecond base metal composition and aluminum. When included, the particles32 are formed of an alloy of the second base metal composition and oneor more austenite-stabilizing elements and/or one or moreferrite-stabilizing elements. For example, atoms of Al and one or moreof austenite-stabilizing elements (Mn, Ni, C, N, Cu and Co), and/or oneor more of ferrite-stabilizing elements (Cr, Mo, Si, Ti, Nb, V and W)can be dissolved, or directly incorporated, in the lattice (e.g., abody-centered cubic lattice or a face-centered cubic lattice of thesteel composition) of the second base metal composition, e.g.,substitutionally and/or interstitially. The atoms of Al and one or moreof austenite-stabilizing element can also be clustered, e.g., formprecipitates, within a matrix of the second base metal composition.However, embodiments are not so limited, and alternative embodiments arepossible, where atoms of Al and one or more of austenite-stabilizingelements and/or ferrite-stabilizing elements are incorporated in thesecond base metal composition in the form of a compound, e.g., aninorganic compound other than an alloy, e.g., silicates, titanates,carbonates, halides, phosphates, sulfides, hydroxides, fluorides andoxides.

Referring now to the welding wire electrode 30C of FIG. 3C, particles 36a, 36 b in the core 38 c have different compositions. In someembodiments, particles 36 a, 36 b contain different elements. In someother embodiments, particles 36 a, 36 b contain the same elements atdifferent concentrations of one or more of the constituent impurities.In the following, while two particles 36 a, 36 b having differentcompositions are illustrated, one or more additional particles can beincluded, where each particle has a different composition.

In the welding wire electrode 30C, the particles 36 a, 36 b, Al and theone or more of austenite-stabilizing elements and/or ferrite-stabilizingelements can be present in different atomically bonded forms. In someembodiments, Al and one or more of non-volatile austenite-stabilizingelements (Mn, Ni, C, Cu and Co), and/or one or more offerrite-stabilizing elements (Cr, Mo, Si, Ti, Nb, V and W), can bepresent in particles 36 a, 36 b in pure elemental form. In theseembodiments, Al and the one or more of austenite-stabilizing elementsand/or ferrite-stabilizing elements can be present in a mechanicalmixture with the base metal composition. In some other embodiments,atoms of the Al and the one or more of austenite-stabilizing elementsand/or ferrite-stabilizing elements are alloyed with atoms of the basemetal composition in the particles 36 a, 36 b. In some otherembodiments, Al and the one or more of austenite-stabilizing elementsand/or ferrite-stabilizing elements are clustered in the particles 36 a,36 b, e.g., in the form of precipitates, within a matrix of the basemetal composition. In these embodiments, the cores of the precipitatescomprise pure elements, while the outer surfaces of the precipitates arebonded with the atoms of the matrix. Yet other embodiments are possible,where Al and the one or more of austenite-stabilizing elements and/orferrite-stabilizing elements form nonmetallic compounds, e.g.,silicates, titanates, carbonates, halides, phosphates, sulfides,hydroxides, fluorides and oxides that form a mixture, e.g., a mechanicalmixture, with the base metal composition.

Still referring to FIG. 3C, different particles 36 a, 36 b can havedifferent compositional arrangements. In some embodiments, all particles36 a, 36 b include a second base metal composition (e.g., any of thesteel compositions described supra) and Al and one or more ofaustenite-stabilizing elements (Mn, Ni, C, N, Cu and Co) and/or one ormore of ferrite-stabilizing elements (Cr, Mo, Si, Ti, Nb, V and W), butat different concentrations. In some other embodiments, some particles,e.g., particles 36 a include a second base metal composition while notincluding one or both of austenite-stabilizing elements andferrite-stabilizing elements, while other particles, e.g., particles 36b include one or both of austenite-stabilizing elements andferrite-stabilizing elements. In some other embodiments, some particles,e.g., 36 a do not include a second base metal composition whileincluding one or both of austenite-stabilizing elements andferrite-stabilizing elements, while other particles 36 b include both asecond base metal composition and one or both of austenite-stabilizingelements and ferrite-stabilizing elements. In some other embodiments,some particles 36 a include a second base metal composition and includeone or both of austenite-stabilizing elements and ferrite-stabilizingelements, while other particles 36 b do not include a second base metalcomposition while including one or both of austenite-stabilizingelements and ferrite-stabilizing elements. In some other embodiments,some particles 36 a do not include a second base metal composition whileincluding one or both of austenite-stabilizing elements andferrite-stabilizing elements, while other particles 36 b include asecond base metal composition while not including one or both ofaustenite-stabilizing elements and ferrite-stabilizing elements. In someother implementations, no particles include a second base metalcomposition while all particles 36 a, 36 b include one or both ofaustenite-stabilizing elements and ferrite-stabilizing elements atdifferent concentrations.

In the above with respect to FIGS. 3A-3C, the welding wire electrodes30A-30C have been described without a particular reference to aparticular suitability for different welding processes among, e.g.,GMAW-C or FCAW. As described above, unlike metal-cored electrodes(GMAW-C), cored electrodes used in flux-cored arc welding (FCAW)additionally includes fluxing agents designed to provide protection forthe weld pool and the weld bead against atmospheric contamination duringwelding, at least partially in lieu of a shielding gas. The fluxingagent forms a slag for flux-cored arc welding (FCAW). In FCAW, thematerial of the flux is not intended to be incorporated into the finalweld bead. Instead, the flux forms a slag, which is removed aftercompletion of welding. Thus, while metal-cored electrodes may notinclude fluxing agents, welding wires configured for FCAW includesfluxing agents.

It will be appreciated that metal-cored electrodes and flux-coredelectrodes are further distinguishable based on the resulting beadcharacteristics. According to various embodiments, metal-coredelectrodes descried herein produce slag islands on the face of theresulting weld bead. In contrast, flux-cored electrodes produceextensive slag coverage of the face of the resulting weld bead. Forexample, slag islands produced by metal-cored electrodes may cover lessthan 50%, 30% or 10% of the surface area of the weld bead. In contrast,slags produced by flux-cored electrodes may cover more than 50%, 70% or90% of the surface area of the weld bead. In the following, embodimentsin which the amount and the arrangement of Al and the one or more ofaustenite-stabilizing elements and/or ferrite-stabilizing elements maybe more advantageous when present in the cores of flux-cored electrodes,including FCAW-S and FCAW-G.

FIG. 3D is a schematic illustration of a welding wire electrode wire 30Dconfigured to serve as an electrode during FCAW. Similar to theelectrode wire 38 c described above with respect to FIG. 3C, the weldingwire 30D includes a sheath 34 formed of a first base metal that caninclude any one of the steel compositions described above. The weldingwire 30D additionally includes a core 38 d having one or more differentparticles 36 a or 36 b, according to any one or combination ofconfigurations described above with respect to the particles 32 in FIG.3B or the particles 36 a, 36 b in FIG. 3C. In addition, in theillustrated embodiment of FIG. 3D, the core 38 d of the welding wireelectrode 30D additionally includes one or more non-metallic particles36 c which include fluxing or slag-forming agents, according toembodiments.

Without being bound to any theory, the one or more non-metallicparticles 36 c, which can include fluorine-containing compounds and/oroxygen-containing compounds, can modify the properties of the slag toimprove the shape of the bead, e.g., to reduce the tendency of gastracking on the formed weld bead. For example, gas tracking, which is aphenomenon observed wherein craters resembling worms are observed on thesurface of the weld bead, may be reduced when fluxing agents arepresent. Without being bound to any theory, gas tracking can beobserved, e.g., in fast freezing slag systems (rutile based) where theslag solidifies much faster than the weld pool. Due to the rapidsolidification of the slag, the gas evolving from the molten weld ispartially trapped and thus forms craters on the weld bead surface.

Without being bound to any theory, some fluxing agents includingfluorine-containing compounds and/or oxygen-containing compounds canalso reduce the melting point of slag. The lower melting point of theslag allows the slag to remain molten for a longer time thereby allowingmore time for gases to evolve from the molten weld and to dissolve inthe slag. The inclusion of fluorine in the slag can also promote theformation of HF, thereby reducing hydrogen from the weld, whichdecreases the partial pressure of hydrogen in the weld system toreducing the incidence of gas tracking.

In particular embodiments in which the welding wires are particularlyadapted for a FCAW-S processes, a slag system based on an aluminumdeoxidizing and denitridizing agents can be particularly beneficial. Inthese embodiments, aluminum enters the weld pool and forms a fluxingagent which includes aluminum oxide, which has a relatively high meltingtemperature. The high melting-temperature aluminum oxide can be combinedwith low-melting-temperature elements in the flux, to form an effectiveslag system. The slag elements including aluminum oxide can melt duringwelding and float to the top of the molten weld pool, protecting theprocess from atmospheric contamination.

FCAW-S has a relatively high tolerance for nitrogen, and the slagsystems make this possible. The aluminum molecules attract oxygen andnitrogen atoms, which connect to form aluminum oxides and nitrides. Thusformed aluminum oxide-based slag system having a high-melting-point(that is, fast-freezing) and lightweight float to the weld surfacequickly. In effect, the slag system transforms oxygen andnitrogen—potential contaminants—into chemical compounds that protect theweld.

Many FCAW-S wires can employ a basic system or an acidic system. Inbasic systems, fluorine-containing compounds work together with thealuminum compounds. In acidic systems, on the other hand, iron oxide canbe employed. The basic systems do a better job of cleaning the weldmetal and tend to be suited for structural-critical work, meetinglow-temperature toughness and other stringent mechanical-propertyrequirements. Acidic systems promote smooth, fast welding. This isbecause, without being bound to any theory, during welding, moleculesare ionized, and specific slag systems are associated with differentlevels of heat to accomplish the ionization. In fluoride systems, arelatively large amount of heat goes into breaking up the molecules toform fluoride bonds. On the other hand, a relatively lower amount ofheat is used to break up the acidic, oxide-based molecules. The quickreaction leads to fast slag-freezing and, ultimately, high depositionrates.

In some embodiments, the non-metallic particles 36 c include inorganiccompounds that include a metal oxide or a metal fluoride of a metalother than Al or Mn.

In some embodiments disclosed herein, when included as part ofnon-metallic particles 36 c, the concentration of fluorine (F) in theelectrode wire can be greater than zero but less than about 5 wt. %,greater than zero but less than about 1.5 wt. %, or greater than zerobut less than about 1.0 wt. %, on the basis of the total weight of theelectrode wire, for instance about 0.1 wt. %.

Other embodiments are possible, where, when included as part ofnon-metallic particles 36 c, the fluorine-containing particles includenon-polymeric or inorganic fluorine-containing compounds, such asaluminum fluoride, barium fluoride, bismuth fluoride, calcium fluoride,manganese fluoride, potassium fluoride, sodium fluoride, strontiumfluoride, polytetrafluoroethylene (such as Teflon®), Na₂SiF₆, K₂SiF₆,Na₃AlF₆ and/or K₃AlF₆; however, it will be appreciated that other oradditional fluorine containing compounds can be used.

Examples of non fluorine-containing non-metallic particles 36 c includetransition metal oxide, e.g., titanium oxide (e.g., rutile, etc.) and/ora transition metal containing compound (e.g., potassium silico-titanate,sodium silico-titanate, etc.), according to embodiments. Generally, whenboth are included, the weight percent of the non fluorine-containingparticles is greater than the weight percent of the fluorine containingcompound, at a ratio between about 0.5-10:1, typically about 0.5-5:1,and more typically about 0.7-4:1, for example.

Example Weldments Formed Using Aluminum-Containing Welding Electrodes

Using various welding wires described above, a weld beads havingparticular compositions can be formed, which can be substantially thesame or substantially different compared to the composition of thewelding wire. In various embodiments, a weld bead (e.g., weld bead 24 inFIGS. 2A, 2B) formed using the welding wire (e.g., welding sires 30A-30Din FIGS. 3A-3D) has iron (Fe) at concentration between about 50 weight %and about 85 weight % and aluminum (Al) at a concentration between about4 weight % and about 8 weight %, or any concentrations of Fe and/or Alof the welding wire described above. In addition, the weld bead includesAl and one or more of austenite-stabilizing elements (Mn, Ni, C, N, Cuand Co) and/or one or more of ferrite-stabilizing elements (Cr, Mo, Si,Ti, Nb, V and W) in concentrations that are substantially the same asthe corresponding concentration(s) of the welding wire as describedabove with respect to FIGS. 3A-3D. The weldment formed using weldingwires and welding methods disclosed herein according various embodimentshave a ferrite number that is between 1 and 125, between 2 and 20,between 20 and 40, between 40 and 60, between 60 and 80, between 80 and100, between 100 and 120, between 120 and 140 or a value within a rangedefined ay any of these values, according to various embodiments.

FIG. 4A is graph 40 illustrating a nickel equivalent versus aluminumcontent for experimentally produced weldments having various ferritenumbers produced from flux-cored electrode wires, according toembodiments. The experimentally produced weldments include first-fourthcompositions 42, 44, 46 and 48 having aluminum contents of 4.8 wt. %,4.9 wt. %, 5.0 wt. % and 5.9 wt. %, respectively, and correspondingNi_(eq) according to Eq. [1] above of 49 wt. %, 41 wt. %, 36 wt. % and35 wt. %, respectively.

FIGS. 4B, 4C, 4D and 4E illustrate SEM micrographs 42 a, 44 a, 46 a and48 a corresponding to the first, second, third and fourth compositions42, 44, 46 and 48, respectively.

Welding Systems Configured for Using Aluminum-Containing WeldingElectrodes

FIG. 5 illustrates an arc welding system 50 configured for use withwelding electrodes discussed supra to deposit weld metal at rates of ˜30lbs./hr. or higher for open-arc welding, according to embodiments. Inparticular, the arc welding system 50 is configured for GMAW, FCAW,FCAW-G, GTAW, SAW, SMAW, or similar arc welding processes that can use awelding electrode comprising an aluminum-containing core, according toembodiments. The arc welding system 50 comprises a welding power source52, a welding wire drive 54, a shielding gas supply 58, and a weldinggun 59. The welding power source 52 is configured to supply power to thewelding system 50 and is electrically coupled to the welding wire drive54 such that the weld electrode wire serves as a first electrode, and isfurther electrically coupled to a workpiece 57 which serves as a secondelectrode, as depicted in detail FIG. 1. The welding wire drive iscoupled to the welding gun 59 and is configured to supply weldingelectrode wire from the electrode supply 56 to the welding gun 59 duringoperation of the welding system 50. In some implementations, the weldingpower source 52 may also couple and directly supply power to the weldinggun 59.

It will be appreciated that, for illustrative purposes, FIG. 5 shows asemi-automatic welding configuration in which an operator operates thewelding torch. However, the metal-cored electrodes described herein canbe advantageously used in a robotic welding cell, in which a roboticmachine operates the welding torch.

The welding power source 52 includes power conversion circuitry thatreceives input power from an alternating current power source (e.g., anAC power grid, an engine/generator set, or a combination thereof),conditions the input power, and provides DC or AC output power to thewelding system 50. The welding power source 52 may power the weldingwire drive 54 that, in turn, powers the welding gun 59. The weldingpower source 52 may include circuit elements (e.g., transformers,rectifiers, switches, and so forth) configured to convert the AC inputpower to a DC positive or a DC negative output, DC variable polarity,pulsed DC, or a variable balance (e.g., balanced or unbalanced) ACoutput. It will be appreciated that the welding power source 52 isconfigured to provide output current between about 100 amps and about1000 amps, or between about 400 amps and about 800 amps, such that weldmetal deposition at rates exceeding about 30 lbs./hr. can be achieved.

The shielding gas supply 58 is configured to supply a shielding gas orshielding gas mixtures from one or more shielding gas sources to thewelding gun 59, according to embodiments. A shielding gas, as usedherein, may refer to any gas or mixture of gases that may be provided tothe arc and/or weld pool in order to provide a particular localatmosphere (e.g., to shield the arc, improve arc stability, limit theformation of metal oxides, improve wetting of the metal surfaces, alterthe chemistry of the weld deposit, etc.). In certain embodiments, theshielding gas flow may be a shielding gas or shielding gas mixture(e.g., argon (Ar), helium (He), carbon dioxide (CO₂), oxygen (O₂),nitrogen (N₂), similar suitable shielding gases, or any mixturesthereof). For example, a shielding gas flow may include Ar, Ar/CO₂mixtures, Ar/CO₂/O₂ mixtures, Ar/He mixtures, to name a few.

The wire drive 54 may include a permanent magnet motor for providinggood control over starting, stopping and speed of wire feed. To enablehigh weld metal deposition rates exceeding about 30 lbs./hr., the wiredrive 54 is configured to provide a wire feed speed between about 50inches per minute (ipm) and about 2000 ipm, between about 400 ipm andabout 1200 ipm, or between about 600 ipm and about 1200 ipm.

In operation, the welding gun 59 receives the welding electrode from thewire drive 54, power from the welding wire drive 54, and a shielding gasflow from the shielding gas supply 58 to perform arc welding on aworkpiece 57. The welding gun 59 is be brought sufficiently close to theworkpiece 57 such that an arc is be formed between the consumablewelding electrode and the workpiece 57, as described supra with respectto FIG. 1. As discussed supra, by controlling the composition of thewelding electrode, the chemistry of the arc and/or the resulting weld(e.g., composition and physical characteristics) may be varied.

Welding Method for Using Aluminum-Containing Welding Electrodes

Referring to FIG. 6, a method of metal arc welding 60 is described. Themethod 60 includes providing 62 a welding wire configured to serve as asource of weld metal during welding. The welding wire comprises a sheathhaving a steel composition and a core surrounded by the sheath. The corecomprises aluminum (Al) at a concentration between about 4 weight % andabout 8 weight % on the basis of the total weight of the welding wire,wherein Al in an elemental form or is alloyed with a different metalelement. The method 60 additionally includes applying 64 a sufficientenergy to produce a steady stream of droplets of molten welding wire.The method 60 further includes depositing 66 the molten droplets onto aworkpiece at a deposition rate exceeding 25 pounds per hour. In aparticular embodiment, depositing 66 comprises depositing under aself-shielded flux-cored arc-welding (FCAW-S) process without ashielding gas as described above, e.g., with respect to FIGS. 2A, 2B.

In the method 60, providing 62 the consumable welding wire comprisesproviding any welding wire described above, e.g., with respect to FIGS.3A-3D.

In the method 60, applying the current 64 includes applying an averagecurrent between about 300 amps and about 600 amps, between about 400amps and about 700 amps, or between about 500 amps and about 800 amps tomaintain an average number of plasma instability events are maintainedbelow about 10 events per second, according to some embodiments.According to some other embodiments, applying the current 64 includesapplying a peak current between about 400 amps and about 700 amps,between about 500 amps and about 800 amps, or between about 600 amps andabout 900 amps.

While certain embodiments have been described herein, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the disclosure. Indeed, the novel apparatus, methods,and systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. Any suitable combination ofthe elements and acts of the various embodiments described above can becombined to provide further embodiments. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A flux-cored welding wire comprising: a coresurrounded by a sheath, wherein the core comprises aluminum (Al), carbon(C), manganese (Mn) and nickel (Ni) in respective amounts such that aweld bead formed using the welding wire has: Mn at a concentrationbetween 18 weight % and 25 weight %, iron (Fe) at a concentrationgreater than 50 weight % or balance, Al at a concentration between 4weight % and 6.5 weight %, wherein the Al of the core is incorporated inthe weld bead as the Al of the weld bead in the form of an alloyingelement, and Ni at a concentration greater than 0 weight % and less than10 weight %, wherein a nickel equivalent defined by 2[Mn]+[Ni]+30[C] ispresent at a concentration of 30 to 50 weight %, wherein [Mn], [Ni] and[C] represent weight percentages of respective elements on the basis ofthe total weight of the weld bead, wherein within respective ranges ofAl and the nickel equivalent, an amount of BCC phase present in the weldbead is proportional to the concentration of Al while being inverselyproportional to the concentration of the nickel equivalent.
 2. Thewelding wire of claim 1, wherein the welding wire is a self-shieldedflux-cored arc welding (FCAW-S) wire, wherein the core comprises afluxing agent comprising an oxide of a metal other than Al or Mn or afluoride of a metal other than Al or Mn.
 3. The welding wire of claim 2,wherein the core comprises: aluminum (Al) at a concentration between 1weight % and less than 5 weight % on the basis of the total weight ofthe welding wire; and manganese (Mn) at a concentration between 30weight % and 60 weight % on the basis of the total weight of the weldingwire, wherein each of Al, Mn and Ni is in an elemental form or isalloyed with a different metal element.
 4. The welding wire of claim 1,wherein the core comprises carbon (C) and nickel (Ni) such that the weldbead formed using the welding wire has carbon (C) at a concentrationgreater than 0 weight % and less than 0.5 weight %.
 5. The welding wireof claim 1, wherein the weld bead has face-centered cubic (FCC)austenite exceeding 30% by volume.
 6. The welding wire of claim 2,wherein the welding wire is configured to form the weld bead having theAl concentration and the Mn concentration when deposited without ashielding gas.
 7. The welding wire of claim 2, wherein the core furthercomprises one or more of ferrite-stabilizing elements selected from thegroup consisting of chromium (Cr), molybdenum (Mo), silicon (Si),titanium (Ti), niobium (Nb), vanadium (V) and tungsten (W) such that theweld bead has a total concentration of the ferrite-stabilizing elementsthat is greater than 0 weight % and less than 10 weight %.
 8. Thewelding wire of claim 2, wherein the core further comprises one or moreof austenite-stabilizing elements selected from the group consisting ofcopper (Cu) and cobalt (Co) such that the weld bead has a totalconcentration of the austenite-stabilizing elements that is greater than0% and less than 10 weight %.
 9. A method of flux-cored arc welding(FCAW), the method comprising: providing the welding wire of claim 1 toserve as a source of weld metal for forming the weld bead duringwelding, the welding wire comprising: the sheath having a steelcomposition, and the core comprising aluminum (Al) at a concentrationbetween 3 weight % and 20 weight % on the basis of a total weight of thewelding wire, wherein Al in an elemental form or is alloyed with adifferent metal element; applying an energy sufficient to produce asteady stream of droplets of molten welding wire; and depositing themolten droplets onto a workpiece to form the weld bead.
 10. The methodof claim 9, wherein the welding wire further comprises manganese (Mn) ata concentration between 10 weight % and 60 weight % on the basis of thetotal weight of the welding wire, wherein Mn is in an elemental form oris alloyed with a different metal element.
 11. The method of claim 9,wherein depositing comprises depositing under a self-shielded flux-coredarc-welding (FCAW-S) process without a shielding gas, and whereinapplying the energy comprises applying a voltage to the welding wire togenerate a plasma arc.
 12. The welding wire of claim 1, wherein the Alin the core is present in the form of a metallic alloy selected from thegroup consisting of AlMg, AlSi, AlZr or AlFe.
 13. The welding wire ofclaim 1, the welding wire comprising: the sheath having a steelcomposition; and the core comprising: Al at a concentration between 3weight % and 20 weight % on the basis of the total weight of the weldingwire, wherein Al is in an elemental form or is alloyed with a differentmetal element.
 14. The welding wire of claim 13, wherein the corefurther comprises manganese (Mn) at a concentration between 10 weight %and 60 weight % on the basis of the total weight of the welding wire,wherein Mn is in an elemental form or is alloyed with a different metalelement.
 15. The welding wire of claim 14, wherein the core furthercomprises one or more of: copper (Cu) at a concentration greater thanzero weight % and less than 10 weight % on the basis of the total weightof the welding wire; and cobalt (Co) at a concentration greater thanzero weight % and less than 10 weight % on the basis of the total weightof the welding wire, wherein a total concentration of the one or more ofCu and Co is greater than zero weight % and less than 10 weight % on thebasis of the total weight of the welding wire.
 16. The welding wire ofclaim 15, wherein the welding wire further comprises one or more of:carbon (C) at a concentration greater than zero weight % and less than2.5 weight % on the basis of the total weight of the welding wire; andnitrogen (N) at a concentration greater than zero weight % and less than2 weight % on the basis of the total weight of the welding wire.
 17. Thewelding wire of claim 16, wherein concentrations of Mn, Ni, C, N, Cu andCo in the welding wire are such that that2[Mn]+[Ni]+30[C]+20[N]+0.3[Cu]+0.3[Co] is between 10 weight % and 80weight %, wherein [Mn], [Ni], [C], [N], [Cu] and [Co] represent weightpercentages of respective elements on the basis of the total weight ofthe welding wire.
 18. The welding wire of claim 1, wherein the weld beadhas a ferrite number between 1 and
 125. 19. The welding wire of claim 1,wherein the weld bead further comprises Cr at a concentration between0.1 weight % and 0.5 weight %.
 20. The welding wire of claim 1, whereinthe concentration of Ni is between 2 weight % and 10 weight %.